The present invention relates to a process and apparatus for the incineration of particulate solids and particularly, biological waste materials with low caloric values. The invention is further directed to a process and apparatus for incinerating previously dried solid particulates, such as municipal sludge, with reduced formation of sintered ash.
Various processes and devices have been developed for incinerating solid particulate materials for various purposes. In particular, municipal waste and sewer sludge generally must be incinerated before disposal in a landfill. The environmental regulations in many countries limit the amount of organic material which can be present in the sludge prior to disposal. Accordingly, various efforts have been proposed to incinerate municipal waste material and sewer sludge to comply with the regulations.
One example of a known process for incinerating waste materials is disclosed in WO 92/14969. This publication discloses a process for feeding finely ground, previously dried sludge into a brick lined combustion chamber, together with a supply of primary combustion air. The furnace is a cyclone combustion chamber having a lower section where the incineration of the solid material takes place. A predetermined amount of moist air with a reduced oxygen content is fed into the combustion chamber to inhibit the sintering of the ash. The ash discharge area of the combustion chamber is cooled using the moist air. The amount of air needed as the primary combustion air and the secondary source of moist air is typically preset for a specific furnace size. The heat output of the furnace is regulated by adjusting the amount of the solid material being incinerated in relation to the fixed amount of the primary combustion air. This device has several disadvantages and is not completely efficient in incinerating solid materials. For example, the process disclosed in this publication is generally difficult to regulate and the output of the incinerated material can be adjusted over a very small operating range. Furthermore, fluctuations in the level of solid material being incinerated and the caloric value of the solid material produces inconsistent results in the incineration of the solid material.
Accordingly, there is a continuing need in the industry for improved processes and apparatus for incinerating solid materials.
The present invention is directed to a process and apparatus for the incineration of particulate solid materials. More particularly, the invention is directed to a process and apparatus for incinerating biological waste materials with low caloric value with a reduced output of sintered ash.
Accordingly, a primary object of the invention is to provide a process and apparatus for incinerating solid materials containing organic matter, such as sewage sludge, in a rapid and efficient manner.
Another object of the invention is to provide a process and apparatus for incinerating organic materials at low temperatures and to incinerate the materials having a lower ash fusion point without ash sintering.
A further object of the invention is to provide a process and apparatus for incinerating organic materials in a furnace and to remove the ash more effectively from the exhaust gas stream.
A still further object of the invention is to provide a process and apparatus for incinerating organic materials in a furnace and for maintaining a temperature of about 1100xc2x0 C. or less, and preferably about 850xc2x0 C.
Another object of the invention is to provide a process and apparatus for incinerating solid particulate materials by blowing a mixture of the solid materials and a sub-stoichiometric proportion of fresh air into a combustion chamber of a furnace.
Another object of the invention is to provide a process and apparatus for incinerating solid particulate materials where the solid material is incinerated in a first combustion zone containing a deficiency of oxygen followed by feeding additional air to a second combustion zone to provide an excess of oxygen and to further incinerate the solid particulate materials.
A further object of the invention is to provide a process and apparatus for incinerating solid materials containing organic matter with reduced formation of carbon monoxide.
Another object of the invention is to provide a process and apparatus for incinerating solid particulate materials containing organic matter where a second source of moist air with a reduced oxygen content compared to the primary combustion air is fed into the furnace to maintain the operating temperature of the furnace at about 850xc2x0 C.
Another object of the invention is to provide a process and apparatus for feeding recycled moist air from a drying plant, and feeding the moist air into the furnace for incinerating solid particulate materials.
Another object of the invention is to provide a cyclone furnace having an annular shaped inlet tube for feeding secondary air into the combustion zone of the furnace in an axial direction.
A further object of the invention is to provide an apparatus for incinerating solid materials where the furnace includes a centrally located feed tube extending axially through the furnace and the feed tube having a plurality of openings therein for supplying a secondary air source to the combustion zone.
The objects and advantages of the invention are basically attained by providing a process for incinerating solid particulate materials comprising the steps of: introducing a feed mixture into a first combustion zone of a furnace, the furnace having a lower end and an upper end defining a primary combustion chamber, the feed comprising the solid particulate material and a first source of combustion air in an amount less than a stoichiometric amount needed to completely incinerate the particulate material; and incinerating the solid particulate material in a first incinerating stage in the primary combustion zone in an atmosphere containing less than a stoichiometric amount of air to inhibit the formation of sintered ash.
The objects and advantages of the invention are further attained by providing an apparatus for incinerating solid particulate materials comprising a furnace wall defining a primary combustion chamber and having a lower end and an upper end; a burner coupled to the furnace wall for introducing hot combustion gases into the primary combustion chamber; a first feed inlet for feeding a feed mixture into a first combustion zone in the primary combustion chamber, the feed mixture including a solid particulate material and a first source of combustion air in less than a stoichiometric amount needed for complete combustion of the solid particulate material; and a second feed inlet for feeding a second source of air into the primary combustion chamber.
The objects and advantages are also attained by providing a furnace for incinerating a solid particulate material comprising: at least one side wall, a bottom wall, a top wall, and an intermediate wall extending substantially perpendicular to the side wall in an inward direction toward an axial center of the furnace, the intermediate wall having a throat opening concentric with a center axis of the furnace and defining a primary combustion chamber in a lower portion of the furnace and a secondary combustion chamber in an upper portion of the furnace; a feed inlet device in the side wall for feeding a feed mixture tangentially into the primary combustion chamber, the feed mixture including a solid particulate material and combustion air in less than a stoichiometric amount needed for complete combustion of the particulate material; and at least one feed pipe for feeding a supply of fresh air into the center of the primary combustion chamber in an amount to cool the primary combustion chamber at a temperature of about 850xc2x0 C.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.